How the central nervous system selects patterns of muscle activity is an important but unanswered question. The long-term objective of this project is to describe the patterns of muscle activity that produce natural arm movements. In this project, electromyographic activity will be recorded from several arm muscles. The specific aims of the proposed project are: 1. To quantify the waveform of the muscle activity that produces a pointing movement. 2. To determine whether pointing movements are produced by a relatively small number of basic waveforms of activity in each muscle. 3. To test the hypothesis that the nervous system produces pointing movements with various characteristics by scaling or shifting the basic waveforms of muscle activity. The specific aims will be accomplished in a series of 4 experiments. In all 4 experiments, standing human subjects will point at stationary targets in 3-dimensional space. In different experiments, the movements will be of various distances, velocities, forces, or directions. for each muscle, the waveform of the electromyographic activity will be quantified by decomposition into component waveforms. The results of the proposed experiments will improve our knowledge of the fundamental patterns of neural activity that produce normal movements. Knowledge of these normal patterns is essential for the understanding of movement disorders and the development of physical therapy.